Primary Amine Functionalization of Alkoxysilanes: Synthesis, Selectivity, and Mechanistic Insights

We report a highly
selective substitution of silicon-bound methoxy
groups by primary lithium amides. This unusual reactivity is possible
because of the formation of particularly stable lithium methoxide,
which compensates for the decreased Si–N bond enthalpy compared
to Si–O bonds. In contrast to substitution reactions on halosilanes,
highly selective monosubstitutions under mild conditions are possible,
even in the presence of further reactive methoxy groups. A combination
of experiments and density functional theory calculations was carried
out in order to get an extensive understanding of the reaction. The
calculations reveal a possible reaction mechanism with considerably
low activation barriers and the entry of the nucleophile to be the
rate-determining step. The low activation energies allow for the substitutions
to be carried out at low temperatures, therefore preventing side reactions
from occurring. The presented investigations expand the view of fundamental
transformation processes on silicon and give access to a wide variety
of functionalized silicon-based building blocks for various fields
of chemistry.